Hydrogen peroxide has heretofore been manufactured by the electrolysis of ammonium hydrogensulfate solution, but recently a process for its manufacture using anthraquinone is being widely adopted. The process for manufacturing hydrogen peroxide using anthraquinone is what is called "anthraquinone process", in which as the working solution use is made of a solution obtained by dissolving an alkylanthraquinone in a suitable solvent or a mixture of solvents. In this process hydrogen peroxide is obtained in such a way that first hydrogen gas is blown into the working solution so as to reduce the alkylanthraquinone in the solution to alkylanthrahydroquinone, and then, into the resulting solution is blown an oxygen-containing gas to effect oxidation, whereby the alkylanthrahydroquinone is again oxidized to regenerate the alkylhydroquinone and at the same time hydrogen peroxide is generated. While the hydrogen peroxide thus produced is recovered by extraction with water from the working solution, the working solution is circulated for rense.
As the alkylanthraquinone used in the above described process there may be mentioned 2-ethylanthraquinone, 2-t-butylanthraquinone, 2-amylanthraquinone, etc., but among them 2-amylanthraquinone (hereinafter referred to as "AMQ") is the most useful compound because of its high solubility in the working solution.
Thus, the AMQ now used in the industry is always a mixture of 2-t-amylanthraquinone (hereinafter referred to as "t-AMQ") and 2-s-isoamylanthraquinone(hereinafter referred to as "s-AMQ"), and such a situation indeed stems from the fact that the 2-(amylbenzoyl)benzoic acid itself which is the starting material of preparation of AMQ, is a mixture of 2-(t-amylbenzoyl)benzoic acid (hereinafter sometimes referred to as "AMB acid") and 2-(s-isoamylbenzoyl)benzoic acid (hereinafter referred to as "s-AMB acid"). That is to say, in the process for preparation of AMB acid, wherein t-amylbenzene is reacted with phthalic anhydride in the presence of Lewis acid, it is impossible to obtain a mixture containing more than 55% of t-AMB acid, so that also in the AMQ prepared from such AMB acid the content of t-AMQ cannot be more than 55% as a natural consequence. This is because when t-amylbenzene and phthalic anhydride react in the presence of Lewis acid, portion of the t-amyl radical is converted to s-isoamyl radical by isomerization.